1. Field of the Invention
The present invention relates to a multi-layer network which is controlled in a unified manner by photonic cross connects, routers, SDH (Synchronous Digital Hierarchy) devices or the like. In particular, the present invention relates to GMPLS (Generalized Multi Protocol Label Switching).
The present application is based upon patent applications Nos. 2002-060435, 2002-060449, 2002-060473, 2002-060477, 2002-060510, 2002-060513, and 2002-060525 filed in Japan, the contents of which are hereby incorporated herein by reference.
2. Description of the Related Art
In recent years, multi-layer networks which have become prevalent can control the photonic cross connects, routers, SDI devices and the like utilized therein in a unified manner. An example of this kind of multi-layer network is shown in FIG. 27. In the example of FIG. 27, a lower layer network consisting of a plurality of photonic cross connects 60 through 76 and transmission lines is connected between the routers 51 through 58. Network topology information is retained in each of the routers 51 through 58. However, this network topology information does not go so far as to include topology information related to the lower layer network; the lower layer network is treated as a single transmission line. In other words, as shown in FIG. 28, the topology information which is retained in the routers 51 through 58 is topology information between these routers themselves, and the existence of the photonic cross connects which make up the lower layer network is not recognized by the routers.
When any of the nodes in this type of multi-layer network, such as photonic cross connects, routers, SDH devices and the like, has detected an obstruction, there is a protocol that it should emit an LSA (Link State Advertisement) packet to the surrounding nodes, and, when any of the routers receives such an LSA packet, it updates the topology information which it retains itself, and it establishes an alternate route which detours around the point of the obstruction.
With a lower layer network of this type of multi-layer network, when an obstruction occurs, obstruction restoration measures, such as establishing an alternate route to detour around the point of this obstruction or the like, can often be executed quickly. However, since it is not possible to recognize from the routers the fact that this type of obstruction restoration measure has been executed by the lower layer network, when an LSA packet arrives, updating of the topology which they themselves retain is quickly performed, and an alternate route is established.
On the other hand, the lower layer network quickly executes the obstruction restoration measures, and then emits an LSA packet to show that the obstruction restoration has been completed. When the routers receive this LSA packet, for a second time, they perform updating of the topology information which they themselves retain, and they perform route establishment again.
In this manner, when a conventional obstruction restoration control technique is applied in its current form to a multi-layer network, the number of cases in which the routers perform updating of topology information and establish alternate routes which quickly become invalid increases, with the result that an increase of the processing load is entailed. In particular, the processing load required for route calculation becomes great, and bad influences may be apprehended, such as deterioration of the processing speed for other processes which are performed between performing route calculations or the like, so that it is desirable to revise and improve this sort of mode of control in which this type of route calculation ends by being invalid. Accordingly, in a multi-layer network, it is desirable to apply a new obstruction restoration control technique which is different from the conventional obstruction restoration control technique.
Furthermore, for the establishment of an alternate route as described above, the lower layer network performs updating of the topology information which it itself retains, and performs establishment of the alternate route by calculating a routing table according to this new topology information.
In this manner, when a conventional obstruction restoration control technique is applied in its current form to a multi-layer network, the routers frequently rewrite the topology information to new topology information although after an extremely short time period it will be necessary to do so again, which is undesirable; and, furthermore, much undesirable new calculation of routing tables and establishment of alternate routes is performed.
As a result, not only is increased processing load imposed upon the routers although this load will shortly become invalid, but repercussions of confusion and congestion take place upon the network as a whole, since alternate routes which have been established are frequently returned back to the original routes after an extremely short time period, thus causing many attempts to be made again to occupy wavelengths which have just been released. Accordingly, it is desirable not to apply conventional obstruction restoration technique in its current form to a multi-layer network, but rather to apply some novel obstruction restoration control technique which should be more suitable for a multi-layer network.